The present invention relates generally to gas turbine engine frames, and more particularly to a fairing for isolating the frame from hot flowpath gases.
In gas turbine engines, support frame structures are provided along the axial length of the engine. Such structural support is typically needed at the turbine stage, especially where bearing supports are provided between turbine stages. The frame structure generally includes inner and outer shells which are connected by frame struts which cross the flowpath of the working fluid. When such frame structure occurs in the hot section of the engine, such as at the turbine, it is desirable to isolate the frame from the hot flowpath gases.
Protection of the frame is accomplished by providing a fairing which includes an inner and outer flowpath wall connected by a hollow airfoil-shaped fairing strut which surrounds the frame strut to provide thermal protection. Because of the arrangement of having a hollow fairing strut surrounding an interior frame strut, various manufacturing and assembly techniques have been suggested in the prior art.
In one approach, the fairing is formed as a one-piece construction using a casting or other fabrication technique. The frame structure is then manufactured or assembled through the one-piece fairing, which is retained as a single piece. Alternately, in another approach, the frame structure is first formed as a one-piece construction either through casting or other fabrication techniques. The fairing is then manufactured around that frame and connected to it as an inseparable assembly.
In each of these prior art approaches, the techniques of manufacturing result in relatively high costs and the assembled structure is complex. The fairing and the frame become inseparable, and, as a result, it becomes difficult to repair portions of either the frame or the fairing when damage occurs to either.
As part of each turbine stage of the gas engine, there is generally provided nozzle guide vanes to direct combustion gases to the turbine and correct the incidence angle to properly drive the turbine. When the frame and fairing are provided adjacent to the turbine, the nozzle guide vanes are generally axially spaced from the fairing and thereby provide an additional axial component spaced from the fairing, whereby the length of the engine is extended and the weight is increased. Since the fairing is cast or assembled as a separate component, it has heretofore not been feasible to integrate the fairing with the nozzle guide vane structure.
Accordingly, it is an object of the present invention to provide an improved frame assembly including a fairing.
Another object of the present invention is to provide a frame assembly which avoids the manufacture and assembly problems of prior art structures.
Another object of the present invention is to provide a frame assembly having a fairing which can be easily manufactured and assembled onto a gas turbine engine while permitting removability for repair and servicing.
Another object of the present invention is to provide a fairing which is formed integrally with a turbine nozzle section to reduce the overall axial length and weight of the gas turbine engine.
Another object of the present invention is to provide a method of manufacturing a frame and fairing assembly for reduced cost and easier assembly and access for replaceability or repair.